1. Field of the Invention
The present invention relates to topical negative pressure (TNP) therapy particularly, though not exclusively, to the control of negative pressure within a wound dressing.
2. Background of the Invention
TNP therapy has assumed great importance in recent years due to the beneficial effects of TNP therapy on a healing wound and also because of the accelerated healing which TNP therapy provides.
Apparatus for TNP therapy ranges from extremely complex apparatus only really suitable for use in a specialised hospital environment to much smaller and simpler, portable apparatus which may be used by an individual patient at home or at work.
The basic principle of TNP therapy is to create a closed cavity over the wound itself by means of a thin, flexible sealing film adhered to the patient's sound skin surrounding the wound; admitting one end of an aspirant conduit into the closed cavity, the conduit being sealed to the flexible film, for example; and connecting a distal end of the aspirant conduit to a vacuum source such as an electrically driven vacuum pump, for example, to create a pressure lower than the surrounding ambient atmospheric pressure within the wound cavity. As is known to the skilled person the lower pressure creates many beneficial therapeutic effects on the wound including increased blood flow to the wound and faster granulation of tissue, for example.
As noted above TNP therapy may be applied by a diverse range of apparatus. However, in general terms the more complex apparatus tends to be used on larger, more serious wounds which require a more intensive and varied treatments by TNP therapy. Examples of apparatus useful in the context of treatment of such larger wounds are given below.
In our co-pending International patent application, WO 2004/037334, apparatus, a wound dressing and a method for aspirating, irrigating and cleansing wounds are described. In very general terms, this invention describes the treatment of a wound by the application of topical negative pressure (TNP) therapy for aspirating the wound together with the further provision of additional fluid for irrigating and/or cleansing the wound, which fluid, comprising both wound exudates and irrigation fluid, is then drawn off by the aspiration means and circulated through means for separating the beneficial materials therein from deleterious materials. The materials which are beneficial to wound healing are recirculated through the wound dressing and those materials deleterious to wound healing are discarded to a waste collection bag or vessel.
In our co-pending International patent application, WO 2005/04670, apparatus, a wound dressing and a method for cleansing a wound using aspiration, irrigation and cleansing wounds are described. Again, in very general terms, the invention described in this document utilises similar apparatus to that in WO 2004/037334 with regard to the aspiration, irrigation and cleansing of the wound, however, it further includes the important additional step of providing heating means to control the temperature of that beneficial material being returned to the wound site/dressing so that it is at an optimum temperature, for example, to have the most efficacious therapeutic effect on the wound.
In our co-pending International patent application, WO 2005/105180, apparatus and a method for the aspiration, irrigation and/or cleansing of wounds are described. Again, in very general terms, this document describes similar apparatus to the two previously mentioned documents hereinabove but with the additional step of providing means for the supply and application of physiologically active agents to the wound site/dressing to promote wound healing.
The content of the above references is included herein by reference.
However, the above apparatus and methods are generally only applicable to a patient when hospitalised as the apparatus is complex, needing people having specialist knowledge in how to operate and maintain the apparatus, and also relatively heavy and bulky, not being adapted for easy mobility outside of a hospital environment by a patient, for example.
Whilst the above examples are mainly relevant to the treatment of larger wounds, there is also a need for the treatment of relatively small wounds where the patient may otherwise be fit and mobile and require treatment outside of a clinical setting such as at home or at their workplace but where the provision of TNP therapy is desirable but nevertheless need to provide controlled conditions in the wound cavity. An example of a suitable apparatus is described in our co-pending UK patent application, GB0712736.8, of common ownership herewith, the content of which is included herein by reference.
An unexpected problem with smaller wounds of relatively low surface area is that they are relatively easy to seal in that they generally may have a relatively large area of sound flesh surrounding them and hence have large sealing borders therearound for the sealing film or drape to seal with and which tends to mitigate against inward air leaks from this area of the dressing. Secondly, even though the sealing films, which are well known to those skilled in the art, tend to be semi-permeable membrane type materials which allow to an extent the passage of gas such as air and water vapour, they do so only to a limited extent which is defined or measured in mass flow per unit area, Thus, since the area of the sealing film above the wound is relatively small, the amount of permitted gaseous flow is small. Because the seal over and around the wound may be very good, it is easy to create a vacuum in the wound cavity which does not decay quickly due to leaks, and therefore, very little or no flow through the aspirant conduit may result and whilst the vacuum is there over the wound, the wound exudate may not be being transported away to a waste canister, for example, and may be stagnating at the wound itself, this being especially so at low levels of negative pressure relative to atmospheric pressure. One important feature of TNP therapy is that the wound exudate fluid is desirably transported away from the wound site. Failure to achieve this efficiently may result in increased risk of infection and in the worst cases may result in back flow of wound exudate into the wound cavity.
However, whether the wound is large or small the fact is that clinicians strive to seal the wound as well as they possibly can so as to prevent bacteria from causing infection. Larger wounds generate greater volumes of fluid and, are therefore, susceptible to filling the wound cavity with fluid. Furthermore, it is possible for the aspiration conduit to fill with exudate fluid resulting in a pressure differential between the wound and the vacuum source due to the viscous drag of the exudate and the height differential between wound and vacuum source.
It is an object of the present invention to mitigate such problems especially, but not exclusively, in portable TNP therapy apparatus and to provide apparatus and a method where reliable flow of wound exudate away from the wound is promoted.